1. Field of the Invention
The present invention relates to a micro-controller, and more particularly to an improved micro-controller to simplify the hardware necessary for accessing an extended memory.
2. Description of the Prior Art
In order to adopt a micro-controller unit (MCU), for example, for use in a controller for a cassette or a floppy disk memory device, logic is embodied by the existence of wiring which increases the need for hardware according to the type of controller. When the controller includes an integrated processor that can program a micro program, a control according to the use may be made simply by changing the micro program and in this circumstance, a micro-controller is needed.
Furthermore, when a read only memory (ROM) used to store a predetermined amount of the micro program is constructed on the semi-conductor chip of the micro controller unit, an exclusive pin controller for the chip can be created, and it is economical for this purpose, to choose a presently available one-chip micro-controller unit having a internal ROM. In this way, a standard application is available by using the above identified floppy disk device and the one-chip micro-controller unit incorporating a micro program.
When the micro-controller unit includes an internal ROM with a given capacity, there exists hardware that can access an extended memory so as to accommodate the possibility of external extended memory. Generally, since the one-chip micro-controller unit has an extra external terminal pin, a control signal, namely, a high or low level signal, can be applied to this pin so as to select, access and control an internal ROM or an external extended memory.